The present invention relates to a digital video tape recorder (hereinafter referred to as digital VTR) having a track format for recording digital video and audio signals in predetermined areas on oblique tracks, and relates to a digital VTR in which the digital video and audio signals are input in the form of a bit stream, and the bit stream is magnetically recorded and played back.
FIG. 93 is a diagram showing a track pattern of a conventional, general consumer digital VTR. Referring to the drawing, a plurality of tracks are formed on a magnetic tape 10, in a head scanning direction inclined to the tape transport direction, and digital video and audio signals are recorded therein. Each track is divided into two areas, a video area 12 for recording a digital video signal and an audio area 14 for recording a digital audio signal.
Two methods are available for recording video and audio signals on a video tape for such a consumer digital VTR. In one of the methods, analog video and audio signals are input, and recorded, using a video and audio high-efficiency encoding means; this is called a baseband recording method. In the other method, the bit stream having been digitally transmitted; this method is called a transparent recording method.
For the system of recording ATV (advanced television) signals, now under consideration in the United States, the latter transparent recording method is suitable. This is because the ATV signal is digitally compressed signals, and does not require a high-efficiency encoding means or a decoding means, and because there is not degradation in the picture quality due to transmission.
The transparent recording system however is associated with a picture quality problem in a special playback mode, such as a fast playback mode, a still mode and a slow mode. In particular, when a rotary head scans the tape obliquely to record a bit stream, almost no image is played back at the time of fast playback, if no specific measure is taken.
An improvement for the picture quality for the transparent recording system recording the ATV signal is described in an article Yanagihara, et al, xe2x80x9cA Recording Method of ATV data on a Consumer Digital VCRxe2x80x9d, in International Workshop on HDTV, 93, Oct. 26 to 28, 1993, Ottawa, Canada, Proceedings, Vol. II. This proposal is now explained.
In one basic specification of a prototype consumer digital VTR, in SD (standard definition) mode, when the recording rate of the digital video signal is 25 Mbps, and the field frequency is 60 Hz, two rotary heads are used for recording a digital video signal of one frame, being divided into video areas on 10 tracks. If the data rate of the ATV signal is 17 to 18 Mbps, transparent recording of the ATV signal is possible with the recording rate in this SD mode.
FIG. 94A and FIG. 94B show tracks formed in a magnetic tape using a conventional digital VTR. FIG. 94A is a diagram showing scanning traces of the rotary heads during normal playback. FIG. 94B shows scanning traces of the rotary heads during fast playback. In the example under consideration, the rotary heads are opposite each other spaced 180xc2x0 apart on a rotary drum, and the magnetic tape is wrapped around over 180xc2x0. In the drawing, adjacent tracks on the tape 10 are scanned by two rotary heads A and B having different azimuth angles, alternately and obliquely, to record digital data. In normal playback, the transport speed of the tape 10 is identical to that during recording, so that the heads trace along the recorded tracks. During fast playback, the tape speed is different, so that the heads A and B trace the magnetic tape 10 crossing several tracks. The arrow in FIG. 94B indicates a scanning trace by head A at the time of five-time fast feeding. The width of arrow represents the width of the region read by the head. Fractions of digital data recorded on tracks having an identical azimuth angle are played back from regions meshed in the drawings, within five tracks on the magnetic tape 10.
The bit stream of the ATV signal is according to the MPEG2 standard. In this bit stream according to the MPEG2 standard, only the intra-frame or intra-field encoded data of the video signal, i.e., the data of intra encoded block (intra encoded block) alone can be decoded independently, without reference to data of another frame or field. Where the bit stream is recorded in turn on the respective tracks, the recorded data are replayed intermittently from the tracks during fast replay, and the image must be reconstructed from only the intra-encoded blocks contained in the replay data. Accordingly, the video area updated on the screen is not continuous, and only the fractions of data of intra coded block are replayed, and may be scattered over the screen. The bit stream is variable-length encoded, so that it is not ensured that all the replay data over the screen is periodically updated, and the replay data of certain parts of the video area may not be updated for a long time. As a result, this type of bit stream recording system does not provide a sufficient picture quality during fast replay in order to be accepted as a recording method for a consumer digital VTR.
FIG. 95 is a block configuration diagram showing an example of recording system in a conventional digital VTR. Referring to the drawing, reference numeral 16 denotes an input terminal for the bit stream, 18 denotes an output terminal for the bit stream, 20 denotes an HP data format circuit, 22 denotes a variable-length decoder, 24 denotes a counter, 26 denotes data extractor, and 28 denotes an EOB (end of block) appending circuit.
To improve the quality of fast replay pictures, the video area on each track is divided into two types of areas. That is, the video area on each track is divided into main areas 30 for recording the bit stream of the ATV signal, and copy areas for recording important part of the bit stream which are used for reconstruction of the image in fast replay. Only the intra-encoded blocks are effective during fast replay, so that they are recorded in the copy areas. To reduce the data further, only the low-frequency components are extracted from all the intra-encoded blocks, and recorded as HP (high priority) data.
The bit stream of MPEG2 is input via the input terminal 16, and output via the output terminal 18, without modification, and sequentially recorded in the main areas 30 on each track of the tape. The bit stream from the input terminal 16 is also input to the variable-length decoder 22, and the syntax of the bit stream of the MPEG2 is analyzed, and the intra-picture data is detected, and timing signals are generated by the counter 24, and the low-frequency components of all the blocks in the intra-picture data are extracted at the data extractor 26. Furthermore, EOBs are appended at the EOB appending circuit 28, and HP data is constructed at an HP data format circuit, not shown. The HP data is incorporated in the recording data for one track, and recorded in the copy areas 32.
FIG. 96A and FIG. 96B show an example of replay system in a conventional digital VTR. FIG. 96A schematically shows normal replay. FIG. 96B schematically shows fast replay.
Separation of data from the magnetic tape during normal replay and fast replay are performed respectively in the following ways. During normal replay, all the bit stream recorded in the main areas 30 is replayed, and the bit stream from the data separation means 34 is sent as the normal replay data, to an MPEG2 decoder, provided outside the replay system. The HP data from the copy areas 32 are discarded. During fast replay, only the HP data from the copy areas 32 are collected, and sent, as fast replay data, to the decoder. At the data separation means 34, the bit stream from the main areas 30 is discarded.
A method of fast replay from a track in which main areas 30 and copy areas 32 is next described. FIG. 97A shows a scanning trace of a head. FIG. 97B shows track regions from which the replay is possible. When the tape speed is an integer multiple of the normal playback speed, if phase-locking control is conducted by an ATF (automatic track following) method or the like for tracking by moving the head itself, the head scanning is in a predetermined phase relationship with tracks having an identical azimuth. As a result, the data replayed by the head A from the tracks recorded alternately by the heads A and B, are fixed to those from the meshed regions.
In FIG. 97B, if the signal having an output level larger than xe2x88x926 dB is replayed by the heads, the data is replayed by one head from the meshed tape regions. The drawing shows an example of nine-time speed replay. If replay of the signals from the meshed regions is ensured at the nine-time replay, the regions are used as copy areas, and the HP data are recorded in the copy areas, so that the reading of the HP data from these regions at this speed is possible. However, reading of these signals at different speeds is not ensured. Accordingly, a plurality of areas need to be selected for the copy areas, so that the replay signals can be read at different tape speeds.
FIG. 98 shows regions where the copy areas overlap for a plurality of different replay speeds. It shows examples of scan regions for three different tape speeds, for cases where the head is in synchronism with an identical-azimuth track. The scan regions where the reading by the head is possible at different tape speeds overlap, at some of the regions. By selecting the regions at which the overlapping occurs as the copy areas, reading of the HP data at different tape speeds can be ensured. The drawings show the regions at which overlapping occurs at the fast-forward at four-time, nine-time, and 17-time speed. Theses scan regions are identical to those of feed-forward at xe2x88x922-time, xe2x88x927-time and xe2x88x9215-time high speeds (i.e., rewind at 2-time, 7-time and 15-time speeds).
Even though there are overlapping regions for different tape speeds, it is not possible to determine a recording pattern so that identical regions are always traced at different speeds. This is because the number of tracks crossed by the head differs depending on the tape speed. Moreover, it is necessary for the head to be capable of starting tracing at whichever identical-azimuth track. For this reason, identical HP data is repeatedly recorded over a plurality of tracks, to solve the above problem.
FIG. 99 shows examples of scanning traces of the rotary head at different tape speeds. Regions 1, 2 and 3 are selected from among the overlapping regions for five-time and nine-time speeds. If identical HP data are repeatedly recorded over 9 tracks, the HP data can be read at either of five-time and nine-time speeds.
FIG. 100A and FIG. 100B show scanning traces at five-time speed replay. In the illustrated example, identical HP data is repeatedly recorded over five consecutive tracks. As will be seen from the drawings, identical HP data is recorded over the number of tracks identical to the number of times of the tape speed (i.e., 5). In either of case 1 and case 2, either the head A or B can read HP data from corresponding azimuth track. Accordingly, providing the copy areas in each track, in a number identical to the number of times of the tape speed at the fast replay, and repeatedly recording the HP data there, the copied HP data can be read at various speeds, and in either the forward or reverse direction.
In the manner described, the special replay data is recorded in the copy areas, repeatedly, to improve the picture quality during the special replay in the transparent recording system.
FIG. 101 shows a recording format on a track in a conventional digital VTR. Main areas and copy areas are provided in one track. In a consumer digital VTR, a video area in each track has 135 sync blocks (SB), and 97 sync blocks are assigned to main areas and 32 sync blocks are assigned to copy areas. The sync blocks at the regions corresponding to the 4-, 9- and 17-time speed shown in FIG. 98 are selected for the copy areas. The data rate of the main areas is about 17.46 Mbps (97xc3x9775xc3x978xc3x9710xc3x9730), and the data rate of the copy areas where identical data is repeated 17 times is about 338.8 kbps (32xc3x9775xc3x978xc3x9710xc3x9730/17).
FIG. 102A and FIG. 102B show an example of the configuration of a track containing video and audio data.
The magnetic tape of a digital VTR according to the specification (hereinafter referred to as SD specification) defined by the SD mode, a video area of 149 SB and an audio area of 14 SB are provided on both sides of a gap, as shown in FIG. 93, and the video and audio data are recorded in these areas, together with error correction codes. Employed as the error correction codes for the video areas in the SD specification are (85, 77, 9) code (hereinafter referred to as C1 check code) in the recording direction (right-left direction in the drawing), and (149, 138, 12) Reed-Solomon code (hereinafter referred to as C2 check code) in the vertical direction. Employed as the error correction codes for the audio areas are (85, 77, 9) Reed-Solomon code (C1 check code) in the recording direction, like the video signal, and (14, 9, 6) Reed-Solomon code (hereinafter referred to as C3 check) in the vertical direction. Auxiliary data (VAUX data) is recorded in front of and at the back of the video data.
FIG. 103 shows an example of configuration of one sync block on the magnetic tape. As illustrated, the region of 1 SB is formed of 90 bytes, and a header consisting of sync pattern recording region 36 of two bytes, and ID signal region 38 of three bytes are formed at the head end, and recording region 42 for the error correction code (C1 check code, in the example illustrated) of 8 bytes is provided at the back of the data region 40 of 77 bytes. In FIG. 102A and FIG. 102B, the header parts are omitted.
Because the conventional VTR is configured as described above, and special replay data is repeatedly recorded in the copy areas, the recording rate for the special replay data is very low. In particular, the quality of the reconstructed pictures formed during slow replay or fast replay is low.
For instance, if the intra-frame is formed twice a second, the amount of data of intra-encoded blocks of the ATV signal is predicted to be about 3 Mbps. In the prior art, only 340 kbps can be recorded, and the quality of the reproduced picture is very degraded.
Moreover, the data for the respective fast replay speeds is recorded, being dispersed over a wide region. Accordingly, if the track is non-linear, it is difficult to achieve accurate tracking control over the entire data region, and the replay signal from some of the regions may not be of a sufficient level.
Furthermore, during special replay (fast replay, slow replay, still replay and the like), the rotary head crosses a plurality of recording tracks obliquely to pick up the replay data intermittently, as was described above. It is therefore not possible to form error correction block (video data) shown in FIG. 102A and FIG. 102B from the replay data during special replay. That is, during special replay, the error correction using C2 or C3 check code is not performed, but error correction using C1 check code alone is applied to the replay data.
If the error correction using the C1 check code alone is applied, if the symbol error rate 0.01, the error detection probability is 1.56xc3x9710xe2x88x923. This means one error per about 8 sync blocks is detected. Because the replay data output is not stable during special replay, so that the symbol error rate can often be more than 0.01. Moreover, the recording data is variable-length encoded, so that when an error is present, the succeeding replay data cannot be used, leading to degradation in the picture quality. The rate of undetected errors is also about 7.00xc3x9710xe2x88x928. Thus, the frequency of occurrence of undetected errors is high.
Moreover, during fast replay, the data rate is low, and only the low-frequency components are replayed, so that the resolution of the picture is poor.
Furthermore, it is necessary to pick up data for a plurality of fast replay regions in one scanning of the head during fast replay, so that when the track is no-linear, or when the scanning trace is non-linear, the data at the fast replay region where the non-linearity is present cannot be reproduced.
Moreover, since it is necessary to pick up data for a plurality of fast replay regions by one scanning of the head, replay can be performed only at certain speeds. The speed at which replay can be performed is limited, and the number of the replay speeds is small.
Moreover, the rotary speed of the drum of the four-head configuration is half that of the drum of two-head configuration, so that the angle with which the head scanning trace crosses the track is larger, and the replay with the four-head configuration drum from the fast replay region is possible only at a speed half the speed at which the replay with two-head configuration drum is possible from the same fast replay region.
Furthermore, when the level of the replay signal fluctuates, the sync bit and the succeeding ID bits, and the first parity are reproducible, and the succeeding digital data is reproducible only up to its middle, and the rest cannot be reproduced because of the decrease in the level of the replay signal. In such a situation, the errors in the digital data is not detected until the result of the check using the second parity is produced. It is therefore necessary to conduct the predefined calculation for performing the check, and time is spent before the error detection.
Moreover, the amplitude of the replay signal varies periodically because the head crosses the recording tracks, so that burst errors frequently occur, and this cannot be detected easily nor quickly.
Moreover, the data used for fast replay is formed by extracting part of the data of the packets transparent-recorded, so that the length of data for forming a block of image is shorted. For this reason, when recording is made for the region used for transparent recording, disposing sync, ID, header, and packets in a predefined format, the fast replay signal cannot be recorded using the same format. The recording signal format forming means is therefore complicated.
Moreover, the fast replay data is used in common for all the replay speeds, so that the period at which one screen of image data is reproduced and displayed during fast replay at each speed is determined by the time for which the region in the tape longitudinal direction in which one screen for fast replay is recorded. Accordingly, the time for which one screen of image data is reproduced is inversely proportional to the speed. With higher speed, the picture changes quickly, while with lower speed, the picture changes slowly. As a result, the displayed image is easy to see for the viewer.
Furthermore, the region used for recording fast replay signal is limited to the region where reproduction is possible commonly for a plurality of fast replay speeds. Accordingly, the number of sync blocks for recording the fast replay signal is limited to the head scanning traces at the time of highest-speed replay, and the amount of data which can be recorded is small.
Moreover, when considering the fluctuation in the position of the head scanning trace due to fluctuation in the tape transport speed or the drum rotary speed, the region from which the data is reproduced without fail during fast replay is further reduced. This is particularly problematical in connection with fast replay with a higher speed.
The invention has been achieved to solve the problems described above, and its object is to provide a digital VTR with which the picture quality is higher in special replay, such as slow replay, still replay and fast replay.
Another object is to improve the resolution during fast replay.
A further object of the invention is to provide a digital VTR with which a fast replay signal can be reproduced without fail even when the track is non-linear or the scanning trace is non-linear, and which is reliable.
A further object of the invention is to provide a digital VTR with which a fast replay is possible at a large number of speeds, and which is convenient to use.
A further object of the invention is to provide a digital VTR with which a fast replay is possible at the same speed without regardless of whether the drum is of two-head configuration or four-head configuration.
A further object of the invention is to provide a digital VTR which permits detection of burst errors at a short processing time using a means of a simple configuration, and detection of erroneous correction.
A further object of the invention is to enable use of a common recording format for the normal data and the fast replay data, and to thereby simplify the format forming means in the recording system and the ID and header reading means in the replay system.
A further object of the invention is to provide a digital VTR with which a fast replay is possible at a plurality of speeds, and the screen is switched at an interval to provide pictures which are easy to see.
A further object of the invention is to provide a device which can record and replay a maximum amount of fast replay signal at each of the fast replay speeds.
A further object of the invention is to provide a device capable of replaying the fast replay signal without being affected by the fluctuation in the head scanning traces.
A further object of the invention is to provide a device capable of fast replay at a very high speed.
According to one aspect of the invention, there is provided a digital VTR for recording recording data having digital video and audio signals, with error correction codes respectively appended in the recording and vertical directions, in respective predetermined areas on oblique tracks of a magnetic recording tape in a predetermined track format, and replaying from the areas, comprising:
data separating means for extracting data of intra encoded blocks in the form of intra-frame or intra-field blocks from the intra-frame or intra-field encoded, or inter-frame or inter-field encoded digital video signal, and the digital audio signal, contained in an input bit stream;
error correction code appending means for appending error correction code to the data of the intra-encoded blocks extracted by said data separating means; and
recording means for recording the data with the error correction code appended, in the recording areas allocated in the magnetic recording tape to special replay data.
With the above arrangement, when replay signal obtained intermittently by scanning the magnetic recording tape during fast replay or slow replay is used to form a replay picture, it is possible to achieve error correction, and accordingly, even for the replay signal having a low output level and a poor symbol error rate, a special replay picture of a satisfactory quality can be formed by applying error correction.
It may so arranged that the recording means disposes the special replay data recording areas in such recording areas that by scanning the magnetic recording tape once with a rotary head at a predetermined replay speed during replay of the special replay data, the error correction code can be reconstructed.
With the above arrangement, the capacity of the memory required in the error correction decoder for forming an error correction block can be reduced. Moreover, the timings for control over writing and reading of the replay data into or from the memory, and starting the error correction can be synchronized with the rotation of the rotary head, so that the control over the memory and control over the error correction decoder can be simplified, and the overall circuit size can be reduced.
It may so arranged that the recording means disposes the special replay data recorded on the magnetic recording tape, taking error correction block for the respective replay speed as a unit, in recording areas concentrated on oblique tracks of the magnetic recording tape.
With the above arrangement, even where there is non-linearity in the track, its effect can be avoided, and the special replay data can be reconstructed without being influenced by the non-linearity, and a special replay picture of a good quality can be obtained.
It may be so arranged that the error correction code appending means appends, to the special replay data, error correction code set to have a minimum distance identical to that of error correction code appended to the digital video or audio signal.
With the above arrangement, by slightly modifying the error correction decoder for the digital video signal or the digital audio signal, error correction decoding can be achieved, and it is not necessary to add a separate error correction decoder, so that the circuit size can be reduced.
It may be so arranged that the error correction code appending means appends, to the intra-encoded block, error correction code having identical magnitude for each of the replay speeds.
With the above arrangement, special replay data can be decoded using the same error correction decoder for various replay speeds, and the circuit size can be reduced.
It may be so arranged that the recording means disposes the error correction code in such recording areas that by scanning the magnetic recording tape once with a rotary head at a predetermined positive or negative symmetrical replay speed (which may be either of the values corresponding to positive and negative tape transport speeds having the same absolute value) during replay of the special replay data, the error correction code can be reconstructed.
With the above arrangement, maximum use is made of the special replay data recording areas to form error correction blocks. Moreover, it is possible to avoid repetition of the special replay data more than necessary, and the sizes of the error correction blocks for the respective replay speeds can be made uniform, and the overall circuit size can be reduced.
According to another aspect of the invention, there is provided a digital VTR for recording digital video and audio signals in respective predetermined areas on oblique tracks of a magnetic recording tape in a predetermined track format, and replaying from the areas, comprising:
data separating means for extracting intra-encoded data in the form of intra-frame or intra-field data from the intra-frame or intra-field encoded, or inter-frame or inter-field encoded digital video signal the intra-frame or intra-field digital video signal, and the digital audio signals, contained in an input bit stream;
recording means for recording the bit stream in areas for the digital video signal, and recording the intra-encoded data extracted at the data separating means, in areas for the digital audio signal.
With the above arrangement, the intra-frame or intra-field, and inter-frame and inter-field encoded digital video signal and the digital audio signal are input in the form of a bit stream, and the bit stream is recorded in the digital video areas, while the extracted intra-frame or intra-field encoded data only is also recorded in the digital audio areas. In this way, the still replay data and slow replay data are formed.
It may be so arranged that the data separating means extracts the intra-frame or intra-field encoded data packet by packet from the bit stream in which the digital video and audio signals are mixed in the form of packets of respectively constant lengths.
With the above arrangement, intra-frame or intra-field encoded data is extracted packet by packet from the bit stream in which the digital video and audio signals are mixed in the form of packets of respectively constant lengths, so that the still replay data and slow replay data can be separated packet by packet. Accordingly, the bit stream can be recorded without modification, on the magnetic tape.
It may be so arranged that the data separating means extracts the intra-frame or intra-field data macro block by macro block from the bit stream forming the digital video data of one macro block, having a plurality of luminance signal blocks and chrominance signal blocks collectively, each block consisting of 8 pixels by 8 lines.
With the above arrangement, intra-frame or intra-field data is extracted macro block by macro block, so that the still replay data and the slow replay data can be separated macro block by macro block. It is therefore possible to cope with the data, formed taking a macro block as a unit, such as that of progressive refreshing.
The digital VTR may further comprise memory means for storing one frame of field of the intra encoded data extracted by said data separating means, data being read from said memory means at a data rate at which data is recorded in the digital audio signal areas.
With the above arrangement, at least one frame or field of intra encoded data is sequentially written, and read at a data rate at which it is recorded in the digital audio signal areas, so that the data is extracted frame by frame or field by field. Accordingly, a still picture can always be recorded by extracting the data frame by frame or field by field.
The digital VTR may further comprises picture replay means for replaying video data for special replay, such as fast replay, still replay, and slow replay, from the intra-encoded data recorded in the digital audio signal areas.
With the above arrangement, by replaying video data for special replay, such as fast replay, still replay and slow replay, pictures with a high definition can be produced.
According to another aspect of the invention, there is provided a digital VTR for recording recording digital video and audio signals in respective designated areas of oblique tracks in a predetermined track format, and replaying from the areas, comprising:
data separating means for extracting intra-encoded data in the form of intra-frame or intra-field encoded data from the intra-frame or intra-field encoded, or inter-frame or inter-field encoded digital video signal, and the digital audio signal contained in an input bit stream; and
recording means for recording the bit stream in the digital video signal areas, and recording the intra-encoded data extracted by the data separating means in the digital audio signal areas, and in the digital video signal areas.
With the above arrangement, the input bit stream is recorded in the digital video areas, and the intra-frame or intra-field encoded data extracted from the bit stream is recorded in the digital video signal areas and the digital audio signal areas, so that by using both of the digital video signal areas and the digital audio signal areas, special replay data with a good picture quality can be obtained.
It may be so arranged that the recording means records a first low-frequency component of the intra-frame or intra-field encoded data in the digital video signal areas, and records a second low-frequency component of a higher-frequency band than the first low-frequency component, of the intra-frame or intra-field decoded data, in the digital audio signal areas.
With the above arrangement, the first low-frequency component of the intra-frame or intra-field encoded data is recorded in the digital video signal areas, and the second low-frequency component of a higher-frequency band than the first low-frequency component is recorded in the digital audio signal areas. Accordingly, a better picture quality can be obtained, and the special replay image can be obtained even if the data in the digital audio signal areas is not reproduced.
According to another aspect of the invention, there is provided a digital VTR for recording recording digital video and audio signals in respective designated areas of oblique tracks in a predetermined track format, using a rotary drum on which head of two different azimuths are mounted, comprising:
data separating means for extracting a fast replay signal from the normal recording signal;
recording means for recording the fast replay signal in one region in one track per one scanning of the head, of the regions covered by the head traces and in the tracks of identical azimuth;
identification signal recording means for recording an identification signal for identifying the track; and
replay means for replaying the identification signal.
With the above arrangement, the fast replay data can be reproduced from one location in one track per one scanning of the head during fast replay, so that even when the track is non-linear or the scanning trace is non-linear, the head can be scanned with reference to the region at said location where the fast replay data is recorded, and the data can be accurately reproduced.
It may be so arranged that a first recording region is provided in one track of one azimuth in which the fast replay signal is recorded, and a second recording region for recording the fast replay signal is also provided in the track of the other azimuth, and succeeding said one track;
the length of the second recording region is about half the length of the first recording region, and the center of the second recording region within the track is at about the same position as the center of the first recording region within the track.
With the above arrangement, in the case of a drum of two-head configuration, the fast replay signal in the tracks of one azimuth can be reproduced from the first recording region, while in the case of four-head configuration, the fast replay signal in the tracks of both azimuths can be reproduced from the first and second recording regions. As a result, the total amount of fast replay data, given as the sum of the data from the heads of two different azimuths, is the same, and the screen (whole picture) can be formed from the same amount of fast replay data, regardless of the head configuration, during fast replay at the same speed.
As a result, it is possible to obtain a device with which the fast replay speed is not limited by the head configuration, and the fast replay picture quality is identical regardless of the head configuration, and the device is therefore convenient to use.
It may be so arranged that, in the upper and lower end parts of the first recording region which extend out of the region corresponding to the second recording region of the adjacent track of a different azimuth, the signal identical to those in said second recording region is recorded.
With the above arrangement, where the sub-regions formed by equally dividing the first recording region is called A1, A2, A3 and A4, in turn, the signals recorded in the regions A1 and A4 are extracted, and recorded, without modification, in the second recording region, as well. In other words, the fast replay data recorded in the track of a first azimuth is divided equally and the first and fourth quarter data are recorded in the track of a succeeding, second azimuth. The data recorded in the track of the second azimuth can therefore be obtained by simple rearrangement means.
It may be so arranged that the recording means forms the fast replay signal dedicated for the particular fast replay signal for each of the fast replay speeds, and records the fast replay signal at different positions on the magnetic recording tape.
With the above arrangement, the fast replay signals are prepared for the respective fast replay speeds, and the data is configured so that the picture is switched at an interval which facilitates watching of the reproduced picture during fast replay at each speed.
It may be so arranged that the recording means repeatedly records the fast replay signal for (Mxc3x97i)-time speed replay (i=1, 2, . . . n) at predetermined positions in predetermined tracks of consecutive M (M being a natural number) tracks, and repeatedly records the fast replay signal for (Mxc3x97i)-time speed replay, 2xc3x97i times, taking the M tracks as one unit for each speed.
With the above arrangement, the fast replay signal for the predetermined speed is recorded in the predetermined position in the predetermined track, of the consecutive M tracks, and the fast replay signal for the (Mxc3x97n)-time speed replay is repeatedly recorded 2n times, taking the M tracks as a unit. Accordingly, during fast replay, it is sufficient if the control over the drum rotation and the tape transport speed performed in such a manner that the fast replay signal recorded at one location in the M tracks is reproduced. For instance, when the fast replay is effected at (Mxc3x97n)-time speed, compared with the case in which the fast replay data is recorded at one location in Mxc3x97n tracks, the amount of movement to a predetermined track in the state of transition at the time of changing the replay speed is smaller, and the reproduction of the fast replay data at the newly selected speed can be started in a shorter time.
It may be so arranged that the recording means repeatedly records the fast replay signal for 4i-time speed replay (i=1, 2, . . . n) at predetermined positions in predetermined tracks of consecutive four (M being a natural number) tracks, and
said identification signal recording means records three types of frequency signals as pilot signal for tracking control on these four tracks, being in superimposition with the digital data.
With the above arrangement, the fast replay data is disposed taking four tracks as a unit, and the identification signals (such as the three pilot signals f0, f1 and f2 two of which (f1 and f2) may consist of two different frequency signals superimposed on the digital data signal, and the last one of which (f0) may be featured by the absence of any signal superimposed on the digital data signal) for tracking control are recorded, so that, during fast replay, by the use of the identification signal, the desired track can be selected, and the fast replay data recorded in the track can be reproduced.
It may be so arranged that the digital VTR further comprises error correction code appending means for appending the error correction code formed of a predetermined number of sync bits inserted at a predetermined period in the signal sequence recorded in the magnetic recording tape, a predetermined number of ID bits succeeding the sync bits, a predetermined number of first parity bits generated from the ID bits, second parity bits generated from a predetermined number of digital data succeeding the first parity bits, third parity bits generated from a plurality of digital data extending over the sync bits, and fourth parity bits generated from the digital data and positioned at the back of the digital data;
erroneous correction detection means for comparing the fourth parity bits with the first parity bits reproduced by the replay means, and detecting erroneous correction on the basis of the result of comparison.
With the above arrangement, a fourth parity is appended only to the digital data recorded in the sync blocks, and on the basis of the result of the fourth parity check, the burst error in which the digital data is continuously missing in the middle of it can be detected quickly by a relatively simple comparison means.
Moreover, on the basis of such information, the erroneous correction at the error correction decoder in a replay system at the next stage can be detected.
It may be so arranged that the error correction code appending means appends the fourth parity bits only to the fast replay signal.
With the above arrangement, errors can be detected promptly even in a fast replay in which burst errors occur frequently due to the periodical amplitude fluctuation in the replay signal.
According to another aspect of the invention, there is provided a digital VTR for recording digital video and audio signals, in designated areas on oblique tracks of a magnetic recording tape, in a predefined format, using a rotary drum on which heads of two different azimuths are mounted, and replaying from the areas, comprising:
data separating means for extracting digital video signal (hereinafter referred to as fast replay signal) used for fast replay, from a normal recording signal;
recording means for recording the fast replay signals for the respective fast replay speeds, in predefined consecutive regions in a predefined track of a group of four consecutive tracks;
identification signal recording means for recording identification signal for identifying the tracks;
replay means for replaying the recording signal for normal replay, or fast replay signals for +2-time speed replay, or +4N-time speed replay or (xe2x88x924N+2)-time speed replay (N being a positive integer); and
tracking control means for performing tracking control so that the head scans the predefined regions in the predefined track of the four tracks in accordance with the identification signal.
With the above arrangement, four tracks are taken as a unit, and identical pattern is repeated every four tracks, and the data for each fast replay speed is recorded in the specific consecutive sync blocks in specific track, and during fast replay, the tracking is controlled at the specific position on the specific track. As a result, it is possible to increase the recording rate of the fast replay data.
It may be so arranged that the identification signal recording means comprises:
recording means for recording, as said identification signal, pilot signals of two different frequencies alternately, every other tracks; and
the tracking control means includes comparison means for comparing the levels of the identification signals of the two different frequencies contained in the replay signal, while the head is scanning the position corresponding to the center of the area where the fast replay signal for the particular fast replay speed is recorded.
With the above arrangement, during fast replay, by comparing, at a specific timing, the levels of the identification signals of two different frequencies contained in the replay signal, and effecting tracking control on the basis of the result of the comparison, the head scans the areas where the data for the respective fast replay speed is recorded. As a result, even if the there is non-linearity in the track, or the like, it is possible to accurately track the region where the necessary data is recorded.
It may be so arranged that the identification signal recording means comprises:
recording means for recording, as said identification signal, pilot signals of two different frequencies alternately, every other tracks; and
the recording means records sync block numbers together with the fast replay signal;
the tracking control means compares the levels of the identification signals of of the two different frequencies contained in the replay signal, when the sync block number of the predefined sync block in the area where the fast replay speed signal for the particular fast replay speed is recorded. to achieve tracking control.
With the above arrangement, when the predefined sync block number is detected during fast replay, the levels of the identification signals of two different frequencies are compared, to detect the tracking error, and tracking is controlled on the basis of the result of the comparison, i.e. on the basis of the detected tracking error. Accordingly, the head accurately scans the area where the fast replay data is recorded. That is, even if the position at which the fast replay data is recorded is shifted in the longitudinal direction of the tape, the area where the necessary data is recorded can be tracked accurately.
According to another aspect of the invention, there is provided a digital VTR for recording digital video and audio signals, in designated areas on oblique tracks of a magnetic recording tape, in a predefined format, using a rotary drum on which heads of two different azimuths are mounted, and replaying from the areas, comprising:
data separating means for extracting digital video signal (hereinafter referred to as fast replay signal) used for fast replay, from a normal recording signal;
appending means for appending sync byte, ID byte, header byte to the fast replay signal, in the same sync block configuration as said recording signal;
recording means for recording the fast replay signal in areas on tracks, such that during fast replay, only one location on one track of an azimuth identical to the head is covered by the head scanning trace;
identification signal recording means for recording identification signal for identifying the tracks; and
replay means for replaying the identification signal.
With the above arrangement, the areas where normal replay data is recorded, and the areas where fast replay data is recorded have an identical sync block configuration, (with identical sync, ID and header configurations) so that the appending means for appending sync byte, ID byte and header byte in the recording system, and the reading means (including the ID and header reading means) can be used in common.
The digital VTR may further comprise:
input means for inputting a password from outside;
recording means for recording the password together with the digital video signal;
replay means for replaying the password at the time of replay of the digital video signal; and
replay inhibiting means for inhibiting display of the digital video signal unless a correct password is input at the time of replay.
With the above arrangement, it is possible to protect the program or the whole tape from unauthorized replay.
According to another aspect of the invention, there is provided a digital VTR for recording digital video and audio signals, in designated areas on oblique tracks of a magnetic recording tape, in a predefined format, using a rotary drum on which heads of two different azimuths are mounted, and replaying from the areas, comprising:
data separating means for extracting digital video signal (hereinafter referred to as fast replay signal) used for fast replay, from a normal recording signal;
recording means for disposing a fast replay signal for an (Mxc3x97i)-time speed replay (i=1, 2, . . . , n), at predefined positions on predefined tracks of consecutive M tracks (M being a natural number), and repeatedly recording the fast replay signal for (Mxc3x97i)-time speed replay, (2xc3x97i) times;
identification signal recording means for recording identification signal for identifying the tracks on which the fast replay signal is recorded; and
replay means for performing replay at an arbitrary replay speed which is an even-number of times the normal speed, and is lower than the (Mxc3x97n)-time speed, using the fast replay signal recorded for (Mxc3x97n)-time speed replay.
With the above arrangement, the data recorded for (Mxc3x97n)-time speed replay can be all replayed at an even-multiple speed lower than the (Mxc3x97n)-time speed, although the reproduced data may be duplicated.
According to another aspect of the invention, there is provided a digital VTR for recording digital video and audio signals, in designated areas on oblique tracks of a magnetic recording tape, in a predefined format, using a rotary drum on which heads of two different azimuths are mounted, and replaying from the areas, comprising:
data separating means for extracting intra-frame encoded image data, from an input bit stream;
recording means for forming fast replay signals for a plurality of fast replay speeds from the image data, and recording the n1-time fast speed signal in an area therefor, at positions designated according to the corresponding position on the screen of the signals, with the signals corresponding to the edges of the screen being positioned at the ends of the recording region on the oblique track, and with the signals corresponding to the position toward the center of the screen being positioned toward the center of the recording region on the oblique track; and
replay means for performing fast replay at an n2 time speed (n2 greater than n1) by replaying the n1-time fast replay signal.
With the above arrangement, the fast replay signal of the central part of the screen is collectively recorded in the center of the area recording the n1-time fast replay signal. and replay is conducted at a fast replay speed n2, higher than n1.
Accordingly, although the areas from which the signal is replayed is narrowed because of the increase of the replay speed to n2, the central part of the screen can be replayed.
According to another aspect of the invention, there is provided a digital VTR for recording digital video and audio signals, in designated areas on oblique tracks of a magnetic recording tape, in a predefined format, using a rotary drum on which heads of two different azimuths are mounted, and replaying from the areas, comprising:
sync block forming means for forming sync blocks by appending sync bytes to digital signal recorded in the magnetic recording tape at a predetermined interval;
data separating means for extracting a fast replay signal from the normal recording signal;
recording means for sequentially and repeatedly recording n pieces of data Di (i=1, 2, . . . n, n being a natural number) each of which can be recorded in one sync block, over (n+2xc3x97w) consecutive sync blocks Sj (j=1, 2, . . . (n+2xc3x97w)) at identical positions on predefined tracks; wherein n is a maximum number of sync blocks which can always be reproduced from the track regions overlapping with the head scanning traces during m-time speed replay,
w is a minimum natural number which is not smaller than the maximum shift from the reference position at which the head crosses a specific track, during m-time speed repay.
With the above arrangement, the maximum amount of data a head can reproduce from one track at a predefined fast replay speed is recorded repeatedly in the vicinity of the head scanning trace, taking account of the head position fluctuation, the maximum amount of data which is recorded can all be reproduced during fast replay. All the data can be read during fast replay in which the effect of the head position fluctuation is large.
It may be so arranged that the recording means repeatedly records the fast replay signal in (n+2xc3x97w) consecutive sync blocks Sj at an identical sync block position on each track, on at least ni consecutive identical-azimuth tracks.
With the above arrangement, the fast replay signal is repeatedly recorded at identical positions on consecutive tracks, so that the fast replay signal can be replayed whichever track the head begins scanning during fast replay.
Accordingly, control over the head scanning position is simplified, and the fast replay at an arbitrary speed is possible as long as the head passes the predefined track positions.
According to another aspect of the invention, there is provided a digital VTR for recording digital video and audio signals, in designated areas on oblique tracks of a magnetic recording tape, in a predefined format, using a rotary drum on which heads of two different azimuths are mounted, and replaying from the areas, comprising:
sync block forming means for forming sync blocks by appending sync bytes to digital signal recorded in the magnetic recording tape at a predetermined interval;
data separating means for extracting a fast replay signal from the normal recording signal;
recording means for sequentially and repeatedly recording p pieces of data Di (i=1, 2, . . . p, p being a natural number not more than n) each of which can be recorded in one sync block, in (p+L+1) consecutive sync blocks Sj (j=1, 2, . . . (p+L+1)) at the same position in each track, in at least ni tracks of consecutive identical-azimuth tracks in such a manner as to satisfy
ek+1=mod[{ek+pxe2x88x92mod(p+L+1, p)}, p]
Where
ek and ek+1 (integers not less than 1 and not more than p) are the suffixes i to the data D first recorded, where n is the maximum number of sync blocks which can always be reproduced consecutively from the region of the track on the tape overlapping with the head scanning trace during m-time speed replay,
L is the number of sync blocks which is a minimum integer not smaller than (Dxe2x88x92B+C) where C is the difference between the starting positions of the tracks Tk and Tk+1 in the track longitudinal direction,
D is the difference between the positions, in the track longitudinal direction, at which the head crosses with the respective tracks,
B is the length of the region from which the reproduction from one track is possible consecutively, during m-time speed replay, and
mod [a, b] expresses the remainder of a divided by b.
With the above arrangement, the arrangement of data repeatedly recorded on the tracks is such that the different data recorded on two identical-azimuth tracks proximate to each other and crossed by the head during one scanning are reproduced at least once without fail, so that the fast replay data can be recorded with a minimum number repetitions. With the arrangement of data described above, even when the head scanning trace position fluctuates or the head trace phase is shifted, reading of the fast replay data is ensured, and images can be reproduced with a good quality, and much fast replay data can be recorded and reproduced.